An organic electroluminescent element (hereinafter, “electroluminescent” is also referred to as “EL”) is a light-emitting element that comprises a light-emitting layer comprises an organic substance as a light-emitting material, and comprises a pair of electrodes (an anode and a cathode) and the light-emitting layer placed between the electrodes. When voltage is applied to the organic EL element, holes are injected from the anode and electrons are injected from the cathode. The holes and electrons are recombined in the light-emitting layer to emit light.
Studies have been conducted on, for example, an illuminating device that comprises a light-emitting device comprising the organic EL element as a light source. By enlarging the area of each of the layers such as the electrode and the light-emitting layer that constitute the organic EL element, the organic EL element can emit light at a large area and then improve lightness. However, enlarging the area of the element increases a voltage drop at the electrode in operation, which may make the center of the element relatively darker. Thus, enlarging the area of the element may result in apparent nonuniformity in brightness. Under the circumstances, in order to secure a certain level of lightness while inhibiting nonuniformity in brightness, an illuminating device comprising a plurality of organic EL elements the areas of which are enlarged but still enough small to make nonuniformity in brightness invisible to a user has been suggested (see JP 2007-257855 A, for example).
FIG. 9 is a schematic of a light-emitting device 2 in which a plurality of (three in FIG. 9) organic EL elements 1 are connected in series. FIG. 9(1) is a plan view of the light-emitting device 2 and FIG. 9(2) is a cross-sectional view of the light-emitting device 2. The plurality of organic EL elements 1 are usually provided on a supporting substrate 3 on which a driving circuit is formed to drive the organic EL elements 1.
The light-emitting device 2 illustrated in FIG. 9 comprises three organic EL elements 1. These three organic EL elements 1 are arranged on the supporting substrate 3 in a prescribed array direction X to be connected in series. As described above, each organic EL element 1 comprises a pair of electrodes 4 and 5 and a light-emitting layer 6 placed between the electrodes. Hereinafter, one electrode out of the pair of electrodes 4 and 5 that is closer to the supporting substrate 3 is described as a first electrode 4, and the other electrode that is farther from the supporting substrate 3 than the first electrode 4 is described as a second electrode 5. One of the first and second electrodes 4 and 5 works as an anode and the other electrode works as a cathode. Between the first and second electrodes 4 and 5, a prescribed layer that is different from the light-emitting layer 6 may be placed in addition to the light-emitting layer 6 in consideration of element characteristics, easiness of processes, and the like.
As illustrated in FIG. 9, the first electrodes 4 of the organic EL elements 1 are discretely arranged to be spaced at prescribed intervals in the array direction X and therefore they are not in physical connection with each other. In the same manner, the second electrodes 5 of the organic EL elements 1 are discretely arranged to be spaced at prescribed intervals in the array direction X and therefore they are not in physical connection with each other. Thus, there is no physical connection between the first electrodes 4 and between the second electrodes 5.
On the other hand, the second electrode 5 is physically connected to the first electrode 4 of the organic EL element 1 neighboring in the array direction X. Thus, the organic EL elements 1 are connected in series. Specifically, the first electrode 4 is formed so that one end (hereinafter, also referred to as the left end) in one array direction X (hereinafter, “one array direction X” is also referred to as “left” and “the other array direction X” is also referred to as right) of the first electrode 4 extends to overlap the right-side end (hereinafter, also referred to as the right end) of the second electrode 5 of the organic EL element 1 neighboring to the left, and therefore it is physically connected to the first electrode 4 of the organic EL element 1 neighboring to the left. Thus, the second electrode 5 is physically connected to the first electrode 4 of the organic EL element 1 neighboring in the array direction X to constitute a series connection of the organic EL elements 1.